I don't have much to say or offer here other than some nice links to stats sites (below) on the relative popularity of email clients, with mobile and tablet clients making great strides. The stats sites seem to agree that iPhone Mail is the most used, and that iPhone Mail + iPad Mail + Apple Mac Mail together corresponded to nearly 50% of all email client usage in Jan 2014.

The fact is that I have had some problems over the years with Thunderbird - such as strange corruptions of folders during upgrades - but mostly it is ok, and I am committed to it. Certainly I am not compelled to move to Apple's Mac Mail yet.

I am not a fan of web mail email clients but have to use them at times.

I try to avoid email on my iPhone, since - being an IT guy working on computers day and night - I would otherwise never escape the digital world.

My other interest in email clients it the almost impossible task of creating email Newsletters that appear similar enough on every email client, because of differences in respecting Cascading Style Sheet (CSS) standards. See links below for some help.